1. Field of the Invention
The present invention relates to a sheet conveying apparatus and an image forming apparatus including the sheet conveying apparatus. In particular, the present invention relates to an image forming apparatus including a sheet conveying apparatus capable of correcting skew feeding of a sheet to be conveyed.
2. Description of the Related Art
In a typical image forming apparatus, the accuracy of a recording position of an image on a sheet (hereinafter referred to as “recording accuracy”) is one of important factors in terms of maintenance of the image quality. For this reason, when a sheet to be conveyed is skew-fed upon image formation, for example, it is necessary to correct the skew-fed sheet to an appropriate sheet position. Thus, various sheet conveying apparatuses having a skew feeding correction function are proposed as related-art image forming apparatuses to improve the recording accuracy (see U.S. Pat. No. 6,011,948).
For example, in a sheet conveying apparatus disclosed in U.S. Pat. No. 6,011,948, plural pairs of conveying rollers are provided in a sheet width direction orthogonal to a sheet conveying direction, and a shutter member is disposed to be rotatable about a rotation shaft of each conveying roller between the pair of conveying rollers. The shutter member includes an abutting portion against which a sheet abuts. When a leading end of a sheet abuts against the abutting portion, the sheet is loosened by a reaction force from the abutting portion, thereby forming a curved loop. The formation of this loop allows the leading end of the sheet to be aligned in parallel with the sheet width direction orthogonal to the conveying direction, thereby correcting skew feeding. After that, when the shutter member rotates, the sheet is conveyed while the leading end of the sheet is nipped by a nip portion between a pair of conveying rollers in a state of being aligned in parallel with the width direction. In short, the sheet is conveyed in the state where the skew feeding of the sheet is corrected.
In recent years, along with an increasing demand for an improvement in throughput of image forming apparatus, there is a demand for an improvement in sheet conveying speed and a reduction in distance from a trailing end of a preceding sheet to a leading end of a subsequent sheet (hereinafter referred to as “a distance between sheets”). Accordingly, after the preceding sheet passes, it is necessary to return the shutter member to a home position (a position where a leading end of a skew-fed sheet is allowed to abut against the abutting portion to thereby correct skew feeding).
FIGS. 27 and 28 illustrate a shutter member 523 provided in a sheet conveying apparatus of a prior art. As illustrated in FIGS. 27 and 28, the shutter member 523 of the prior art is rotatably supported by a rotation shaft 518a on one side of a pair of conveying rollers 518 and 519. The shutter member 523 guides a sheet S to allow the sheet to pass through a nip portion between the pair of conveying rollers 518 and 519. After that, the shutter member 523 is rotated to return to an abutting position to allow the sheet to pass through the nip portion between the pair of conveying rollers 518 and 519. Therefore, a required minimum distance between sheets is a distance D3 which is obtained by adding a distance D1 from a position where the trailing end of the preceding sheet S passes through the abutting surface of the shutter member 523 to the home position where the skew feeding of the sheet S is corrected, and a distance D2 at which the subsequent sheet S is conveyed to the home position.
Since the shutter member 523 reciprocatingly moves so as to pass through the nip portion between the pair of conveying rollers 518 and 519, the distance D1 is generated and a time Δt is necessary for the shutter member 523 to move the distance D1. On the other hand, the distance D2 is a distance (Δt×V) obtained by multiplying the time Δt necessary for the shutter member 523 to move the distance D1, by a conveying speed V of the sheet S, and the distance increases along with an increase in the conveying speed of the sheet S. Accordingly, the sheet conveying apparatus of the prior art has a problem in that the distance between sheets increases as an increase in the conveying speed of the sheet S, which hinders a further improvement in throughput.
Therefore, the present invention provides a sheet conveying apparatus capable of suppressing an increase in a distance between sheets and improving throughput even when the sheet convey speed is increased, and an image forming apparatus including the sheet conveying apparatus.